Saturday, 30 April 2016

Waiting to die



The bullets that will kill the Great Barrier Reef were fired long ago.

The delay between CO2 emission and its full warming effect is about 40 years. Even a complete elimination of emissions tomorrow will mean we will continue to see warming through to the middle of the century. We are, of course, not going to stop emissions any time soon. We have already committed to continued warming through until the middle of the century.

As the atmosphere warms due to our emissions, other factors will drive variability around that warming trend. While the size of that variation may not increase, the temperatures reached will inexorably rise. That variation will allow people to point at short periods and claim that the warming has stopped or even gone into reverse. They'll be wrong.

We've had the usual idiots writing in to the Cairns Post to argue that the recent high temperatures are just the result of El Nino, but of course they're (willfully?) ignorant on this point. While El Nino is causing a spike, we've given the temperatures reached due to that spike a leg up. A return to neutral or La Nina conditions will see temperatures fall back a bit, but even these will be elevated from what they would otherwise be.

Coral bleaching has struck along the Great Barrier Reef, particularly in the northern section between Cooktown and the Torres Strait. It is less severe the further south you go, but the bleaching extends south past the Great Barrier Reef, with even Sydney Harbour's two species of coral experiencing bleaching. The bleaching also extends around Australia's north to Western Australia.

Footage coming out from Lizard Island is particularly depressing. The above video shows how extensive the bleaching is. The footage of clown anemonefish in their bleached anemone struck me particularly hard. A mix of anger, depression and resignation. The burning of fossil fuels is slowly killing the Reef.

There has been a bit of anger from some quarters about media coverage possibly harming tourism. Some has been poorly worded, especially headlines along the lines of "95% of the Great Barrier Reef is bleached". Metrics are being confused, with reports of the percentage of individual reefs experiencing some degree of bleaching being misunderstood as 95% of the coral is severely bleached or, worse, dead. Things are bad, but not that bad.

A recent report from the Reef and Rainforest Research Centre on the degree of bleaching in the Cairns area of the Reef is being used by some as damage control, though it still makes disturbing reading. They measure percentage of coral cover, and how much of that is unboleached or in four categories of bleaching damage:
1. Upper surface – The least severe bleaching effect where the tips or upper surface of the
corals begin to whiten. Although the whole colony is recorded as bleached, the bleaching is only occurring on the upper surface.

2. Pale/Fluoro – The next most severe category is where the whole colony pales as it begins to lose its photosynthetic zooxanthellae. This will sometimes give the corals a fluorescent appearance. These corals are in a state of stress but still maintain some of their photosynthetic zooxanthellae.

3. Totally white – This is the most severe type of bleaching when the coral polyps will eject their photosynthetic zooxanthellae and the colony will appear totally white. Although the coral polyps are still alive they are in a highly compromised state, unable to produce sufficient energy to maintain normal functions.

4. Recently dead – The coral polyps have died and the remaining calcium carbonate skeleton will become covered with. (sic)
And here's the overview of their findings.

This is the report that some are using to downplay the damage, to put a positive spin on things. While conditions are improving, the event still isn't over. Those black bits on the bars are going to grow larger. The size of those yellow and red segments have me uttering profanities I choose not to use on this blog.

The bars are arranged from southernmost to northernmost, with Agincourt Reefs (center) being about as far as day trippers go out from Cairns. The Ribbon Reefs further north are serviced from Port Douglas and overnight trips. Cairns has escaped comparatively well, with little in the fully bleached and dead categories meaning there's a decent chance of a low mortality rate and some recovery as conditions cool through winter and, one hopes, a return to La Nina or neutral conditions before next summer.

Bleached coral can, when conditions ease, recover in time. The 2002 bleaching event, previously the worst we had had, resulted in about 5% coral mortality. It's too early to say what the mortality rate of the current event will be, but it would be surprising if it's better than it was after 2002.

In the long term the Reef faces further bleaching events. As mentioned above, we are locked in for at least another 40+ years of warming. As that warming continues, the size of an upward spike needed to cause a bleaching event will become smaller and smaller. How many more bleaching events can the Reef survive?

The Reef will change in the years ahead. Heat tolerant species will fill in some of the gaps left by other species dying off. Coral will give way to algae, corallivores will be replaced by herbivores. Some species will be driven extinct, perhaps iconic species like anemonefish. The Reef will survive in some form, but will be greatly impoverished.

If you want to see the Great Barrier Reef, make it soon. The Reef as we know it is waiting to die.

Reference:
Reef and Rainforest Research Centre and Association of Marine Park Tourism Operators (2016) Coral BleachingAssessment on Key Tourism Sites between Lizard Island and Cairns. Reef and Rainforest Research Centre Limited, Cairns


To counter the depressing nature of the above post, here's something more light-hearted:



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